Insulated electric conductor



522320 1%, 19:32. BOVENG 345,041

INSULATED ELECTRIC CONDUCTOR Filed Sept. 16, 1927 Arron/var PatentedFeb. 16, 1932 UNITED STATES PATENT OFFICE HENRIK BOVIN G, 01 NEW YORK,N. Y., ASSIGNOR TO TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N.Y., A CORPORATION OF NEW YORK INSULATED ELECTRIC CONDUCTOR Applicationfiled September 18, 1927. SeriaLNo. 219,908.

This invention relates'to the insulation for electrical conductors. Oneapplication of it is in insulating wire and more particularly to theinsulating of copper wire of the type 5 having a coating of bakedenamel.

When the usual types of enamels, such as black compound and varnishenamels, are applied and baked directly on tinned copper wires, theenamel adheres so firmly to the wire that it is dilficult toremoveunless it is baked very soft or very hard. Either the very soft orthe very hard baking of the enamel coating is undesirable because in theI very soft state the coating is susceptible to mechanical injury and inthe very hard state it becomes brittle and will not stand handling orbending without flaking. Furthermore, in the case of tinnedcopper wirethe baking incident to producing a very hard enamel coating causes thetin to partly alloy with the copper, thereby producing a surface whichis difficult to solder.

The invention in one aspect consists of means between the enamelinsulation and the conductor for facilitating the removal of theinsulation.

In a more specific aspect, the invention comprises applying to. a tinnedwire a priming coating of adhesive/material, such as a varnishcontaining a phenolic condensation product, or a varnish composed of ametallic soap dissolved in a volatile solvent, baking the coating toform an adherent layer, applyingv to the riming coating a coating ofinsulating enamel and baking the double coating at 1 a highertemperature than the baking temperature of the priming coating, tochange the priming coating to a substantially nonadherent layer and forman insulation having the necessary qualities of flexibility, inertnessto solvents and freedom from embrittling 'upon aging. The thin primingcoating has the property of beingmore adherent to the insulating enamelthan to the surface of the wire so that the insulation may be easily andcompletely removed by stripping, by mechanical means, thus leaving thetinned wire in suitable condition for soldering purposes.

A more detailed description of the invention follows and is illustratedin the accompanying drawings.

Fig. 1 illustrates a conductor having a thin priming coating of materialwhich is substantially non-adherent and an outer coating of elasticinsulating enamel.

F ig'. 2 is a cross-sectional view of Fig. 1.

Referring to the drawings, Fig. 1 shows an electrical conductor 10, ofcopper, having a thin coating of tin to form a surface which is easy tosolder. The amount of tin in the coating is necessarily small beingapproximately from one to six milligrams per square inch of conductorsurface. Heavy tin 'coatings are not'suitable for subsequent enamelingbecause the enamel coating is usually baked at a temperature above themelting point of tin, and heavy coatings roduce a suflicient amountofliquid tin in the enamel baking process so that the tin collects indroplets under the enamel applied to the conductor. A thin primingcoating 11 is applied to the tinned conductor or wire 10 and ispreferably of an adhesive material which can be baked to a hardnon-adherent state at a 75 temperature not greater than that used forproducing the usual type of enamel coating in-the adherent flexiblestate.

It has been found that varnishes containing a condensation product ofthe phenol group, such as bakelite varnishes, or a varnish or enamelprepared by dissolving metallic soaps in boiled vegetable oils aresuitable for the-priming coat. By diluting the varnish or enamel with asuitable volatile solvent, the thickness of the priming coating may bevaried from .0002 of an inch to .00005 enameling process. When thepriming coating consists of a varnish containing a phenolic condensationproduct, the baking temperature should be approximately 400 F., whilethe baking temperature of the metallic soap varnish should beapproximately 500 F. This preliminary baking temperature can be changed,however, depending upon the type of varnish used in the priming coatsince the object of this baking is to dry the varnish and .producesufiicient adherence of the varnish to the conductor during subsequentoperations. The conductor is passed through a bath containing an enamelin any suitable manner to form a layer or a plurality of layers ofprotective insulation and finally baked at a suitable temperature fromapproximately 500 to 600 F. The enameling and baking may be performed ina continuous operation in an ovenstructurev such as is disclosed in theHolmes and l larris Patent 1,101,281, dated June 23, 1914. a

The final baking temperature which is higher than the baking temperatureof the priming coating changes the priming coating from a flexibleadherent layer to a substantially non-adherent coating on the conductorsurface. The priming coating is of a fragile character but due to itsadherence to the enamel insulation the two coatings may be easilystripped from the conductor by mechanical means, such as pliers, and thetinned conductor will be in clean condition to soldering operations.

By regulating the thickness of the priming coating, enamel coatings maybe produced varying from the condition of being very ads" herent andtherefore diflicult to remove, to the condition of being quitenon-adherent, easy to 395 171, filed September 25, 1929.

I The invention is not limited to the specific materials entioned forthe priming coating since other materials may be employed which wouldbecome non-adherent continuous priming layers after the insulatingcoating has been applied and treated as described above.

Furthermore, the invention is not limited to the particular method ofbaking since the coatings may be treated by other media to cause thepriming coating to become nonadherent to the conductor.

What is claimed is:

1. The method of forming a coating of insulation on an electricconductor which comprises, applying to the conductor a coating ofadhesive material, applying thereto a coating of insulation, andtreating the insulated conductor to render the inner coatingnon-adherent.

2. The method of forming a coating of insulation on an electricconductor which comprises, applying to the conductor a coating ofadhesive material, applying thereto a coat ing of. insulation, andapplying heat to the insulated conductor to render the innercoatingnon-adherent.

3. The method of forming a coating of insulation on an electricconductor which coniprises, applying to the conductor a coating ofvarnish, applying thereto a coating of insulation, and treatingtheinsulated conductor to render the inner coating non-adherent.

4. The method of forming a coating of insulation on an electricconductor which comprises, applying to the conductor a coating ofvarnish, applying thereto a coating of insulation, and applying heat tothe insulated conductor to render the inner coating non-adherent.

5. The method of forming a coating-of insulation on an electricaLconductor which comprises, applying to the conductor a coating ofadhesive material, applying thereto a coating of. insulating enamel, andtreating the insulated conductor to render theinner coatingnon-adherent. v

6. A method of-forming a coating of insulation on an electricalconductor which com prises, applying to the conductor a coating ofadhesive material, applying thereto a coating of insulating enamel, andapplying heat ios dried and becomes non-adherent when heated asufiieient, amount, applying a second coat- "ing of a differentinsulating material, and

heating the two coatings to render the priming coating non-adherent. z9. The method of forming a coating of insulation on a conductor whichcomprises, ap-

plying a coating of varnish having properties which change within acertain range of temperatures, baking the coating at temperatures etween300 and 500 F., applying a finishing coating of elastic material, andbaking the two coatings at temperatures between 500 and 600 F.

10. The method of forming a coating of insulation on a conductor whichcomprises, applying a varnish containing a phenolic condensationproduct, baking the varnish at a temperature of approximately 400 F.,applying an insulating enamel to said varnish, and baking the varnishand enamel at a temperature ofapproximately 600 F.

11. An electric conductor insulated with baked enamel, comprising. alayer in contact with the conductor for spacing the insulation from theconductor, said layer being non-adherent to the conductor.

12. An electric conductor insulated with baked enamel, comprising alayer of fra ile varnish between the enamel and the cond uctor forfacilitating the removal of the insulation.

V 13. An electric conductor insulated with baked enamel, comprising aphenolic condensation varnish between the insulation and the conductorfor preventing the latter adhering firmly to the former.

14. An electric conductor insulated with baked en amel, comprisinga-layer of varnish containing an einbrittling agent between the enameland the conductor for preventing the adherence of the enamel to theconductor.

15. An insulated conductor having a plurality of coatings of insulatingmaterial thereon, the innermost coating consisting of a thin priminglayer of varnish, said layer being substantially non-adherent to thesurface of the conductor and firmly adherent to the adjacent coating ofinsulating material.

16. An insulated conductor compris' a central wire having a non-adherentriming layer of varnish containing a. pheno ie condensation product, andan outer coating of insulating enamel firmly adherent to saidnon-adherent primin layer.

17; The method 0 forming a coating of insulation on a conductor whichcomprises applying a varnish to the conductor containing a materialwhich is non-adherent when heated to a certain temperature, baking thecoating at a temperature to dry the varnish on the conductor, applyingan insulating enamel to said coating, and baking the varnish and enamelat a temperature of approximatel 600 F. I

18. he method of forming a coating of insulation ona conductor whichcomprises applying to the conductor a riming coating 0 insulatingmaterial which changes from an adherent to anon-adherent state within acertain ran a oftemperatures, baking the priming coating at atemperature below the insulation on a conductor w perature, whereby thevarnish coatin said layers being capable of being transitiontemfi'perature, applying a second coating of a di erent insulatingmaterial, and baking the two coatings at a temperature higher than thetransition temperature of said priming coating.

19. The method of formin a coating of ich comprises applying a coatingof varnish erties which change at high temperatures, baking the coatingto form an adherent layer,

applying a finishing coating of elastic material, and baking the twocoatin at a higher temperature than the first baking teraheres to thefinishing coating more rmly than to the conductor.

20. In an insulated conductor, a layer of insulating varnish adjacent tothe bare conductor composed of material which is substantiallynon-adherent thereto, and a la er of insulating enamel adherent to saidvarnish, easily stripped from the conductor.

In witness whereof, I hereunto subscribe my name this 8th day ofSeptember, A. D.

HENRIK BOVING.

having prop-

